EP0949504A1 - Méthodes pour déterminer des matières condensables dans un volume de gaz et appareils à cet effet - Google Patents

Méthodes pour déterminer des matières condensables dans un volume de gaz et appareils à cet effet Download PDF

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Publication number
EP0949504A1
EP0949504A1 EP98400831A EP98400831A EP0949504A1 EP 0949504 A1 EP0949504 A1 EP 0949504A1 EP 98400831 A EP98400831 A EP 98400831A EP 98400831 A EP98400831 A EP 98400831A EP 0949504 A1 EP0949504 A1 EP 0949504A1
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EP
European Patent Office
Prior art keywords
volume
gas
fact
peltier effect
temperature
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Application number
EP98400831A
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German (de)
English (en)
Inventor
Pascal Ancey
Kunio Ishihara
Jean-Pierre Fontaine
Alain Laroche
Michel Gschwind
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IMRA Europe SAS
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IMRA Europe SAS
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Priority to EP98400831A priority Critical patent/EP0949504A1/fr
Publication of EP0949504A1 publication Critical patent/EP0949504A1/fr
Withdrawn legal-status Critical Current

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N25/00—Investigating or analyzing materials by the use of thermal means
    • G01N25/56—Investigating or analyzing materials by the use of thermal means by investigating moisture content
    • G01N25/66—Investigating or analyzing materials by the use of thermal means by investigating moisture content by investigating dew-point
    • G01N25/68—Investigating or analyzing materials by the use of thermal means by investigating moisture content by investigating dew-point by varying the temperature of a condensing surface

Definitions

  • the present invention relates to methods of determining a magnitude characteristic of a quantity of condensable substances present in a volume of gas, for determining said quantity of condensable substances or a risk of condensation on a surface in contact with the volume of gas, and apparatuses for implementing such methods.
  • Such a method is particularly useful in anticipating the formation of mist on a vehicle windshield.
  • That method consists in using a sensor having a sensitive element which is taken to the temperature of the surface, and in subjecting said sensitive element to temperature oscillations around the temperature of the surface.
  • That method does not make it possible to determine the humidity level of the air present in the cabin of the vehicle.
  • the present invention seeks to provide methods and apparatuses that are particularly simple and low in cost, enabling a magnitude characteristic of a quantity of condensable substances present in a volume of gas to be determined in a manner that is reliable.
  • the invention makes it possible to determine a magnitude that is characteristic of the quantity of water present in the volume of air, and said magnitude can be used directly for controlling a regulator system, e.g. in the cabin of a vehicle.
  • Knowing said magnitude it is also possible to determine the humidity level of the volume of air, or the risk of condensation on a surface in contact with the volume of air.
  • the present invention thus provides, firstly, a method of determining a magnitude characteristic of a quantity of condensable substances present in a volume of gas, the method being characterized by the fact that it consists in:
  • the above method makes it possible to determine a magnitude that is characteristic of the quantity of water present in the air.
  • This magnitude can be used as such for controlling a regulator system.
  • the air temperature as the predetermined temperature, it is possible to deduce therefrom a magnitude characteristic of the relative humidity of the air.
  • the predetermined temperature is that of a surface in contact with the volume of air, it is possible to deduce therefrom a magnitude characteristic of the risk of water condensing on said surface.
  • a pulse width modulated (PWM) signal is generated as the magnitude characteristic of the quantity of condensable substances present in the volume of gas, the modulation of the signal being determined by the times at which the derivative reaches the special point.
  • PWM pulse width modulated
  • the PWM signal may be given:
  • the PWM signal obtained can be used directly to control an air conditioner or heater means for opposing the appearance of mist on the windshield.
  • the PWM signal it is also possible from the PWM signal to calculate the duty ratio thereof and to take said duty ratio as the magnitude characteristic of the quantity of condensable substances present in the volume of gas.
  • an output voltage is generated proportional to the duty ratio of the PWM signal, and said output voltage is used as the magnitude characteristic of the quantity of condensable substances present in the volume of gas.
  • This variant makes it possible to use the method of the invention for controlling conventional regulator devices which are controlled by an input voltage and not by a PWM signal.
  • the special point of the derivative may be selected as the point where the derivative becomes less than a predetermined threshold value.
  • said threshold value is determined by performing the first three steps of the method of the invention in air that has no substances liable to condense at temperatures in the vicinity of the predetermined temperature and at the pressure of the volume of gas under consideration, thereby providing a value for the derivative that is substantially constant and that is taken as the threshold value.
  • the special point of the derivative can be selected as the point at which the derivative is at a maximum.
  • the method of the invention is advantageous in that it can be implemented without requiring the use of digital means, analog means such as a comparator and/or a differentiator being quite sufficient.
  • a comparator signal in order to define the characteristic magnitude on the basis of the point at which the derivative becomes less than the predetermined threshold value, a comparator signal is used whose value is equal:
  • this comparator signal corresponds, in analog form, to the PWM signal as defined above.
  • the reference signal is the voltage across the terminals of another Peltier effect module whose sensitive element is enclosed in a volume of gas that has no condensable substances, said other Peltier effect module being substantially identical to the module whose sensitive element is in contact with the volume of gas, and being subjected to the same temperature cycles.
  • the reference signal is the voltage across the terminals of another Peltier effect module whose sensitive element is covered in a material that is proof against the condensable substances, e.g. a resin that is proof against water vapor, and that is thermally insulating, said other module being substantially identical to the module whose sensitive element is in contact with the volume of gas, and being subjected to the same temperature cycling.
  • a material that is proof against the condensable substances e.g. a resin that is proof against water vapor, and that is thermally insulating
  • the reference signal is the opposite of the voltage across the terminals of another Peltier effect module substantially identical to that whose sensitive element is in contact with the volume of gas, the two modules being subjected to inverse temperature cycles.
  • the sensitive elements of the two Peltier effect modules are subjected to identical temperature oscillations that are offset by half a period, the voltage across the terminals of the module used for measurement during the heating stage being compared with the opposite of the voltage across the terminals of the other module which is in the cooling stage.
  • the reference signal is supplied by a memory in which there has previously been stored the voltage across the terminals of the Peltier effect module during the cooling stage preceding the heating stage.
  • the reference signal is supplied by an electronic circuit having at least one electronic component that is sensitive to variations in temperature, such as a thermistor or a diode, for example, said electronic component being selected so that the reference signal varies as a function of the mean temperature of the circuit in the same manner as the measurement signal from the Peltier effect module whose sensitive element is in contact with the volume of gas.
  • an electronic circuit having at least one electronic component that is sensitive to variations in temperature, such as a thermistor or a diode, for example, said electronic component being selected so that the reference signal varies as a function of the mean temperature of the circuit in the same manner as the measurement signal from the Peltier effect module whose sensitive element is in contact with the volume of gas.
  • the reference signal is delivered by a first electronic circuit which generates a stable signal that does not drift with temperature
  • the circuit powering the Peltier effect module includes at least one electronic component such as a thermistor or a diode, for example, said electronic component being selected in such a manner that any temperature drift of the Peltier effect module causes the electrical properties of the electronic component to be modified, said modification being suitable for compensating the effect of temperature drift on the voltage across the terminals of the Peltier effect module.
  • the present invention also provides a method of determining a quantity of condensable substances present in a volume of gas, characterized by the fact that it consists in implementing the above-described method, in taking the temperature of the volume of gas as the predetermined temperature and in deducing the quantity of condensable substances therefrom by consulting a previously-established chart representing the relationship that exists between the quantity of condensable substances in the volume of gas and said characteristic magnitude.
  • the condensable substance in the volume of gas is water in a volume of air, and the method serves to determine the relative humidity of the volume of air.
  • the present invention also provides a method of determining a risk of condensation on a surface in contact with a volume of gas containing condensable substances, the method being characterized by the fact that it consists in implementing the above-defined method, using as the predetermined temperature the temperature of the surface in contact with the volume of gas.
  • the present invention also provides apparatus for determining a magnitude characteristic of the quantity of condensable substances present in a volume of gas.
  • Such apparatus comprises: a Peltier effect module having a sensitive element placed in contact with the volume of gas, brought to a predetermined temperature, and suitable for being subjected to a temperature cycle around the predetermined temperature, said cycle including both a cooling stage and a heating stage; means for generating a reference signal corresponding to the voltage that would be present across the terminals of the Peltier effect module if its sensitive element were isolated from the volume of gas; a differential amplifier for determining, during the heating stage, the difference between the voltage across the terminals of the Peltier effect module and the reference signal; a differentiator for calculating the time derivative of said difference; and means for defining a magnitude characteristic of the quantity of condensable substances present in a volume of gas on the basis of the special point.
  • the apparatus of the invention includes a PWM signal generator, with the signal being modulated at instants determined by the moments when the derivative reaches the special point.
  • the apparatus includes a converter stage for calculating the duty ratio of the PWM signal and generating an output voltage proportional to the duty ratio.
  • the means for determining the special point of the derivative is a comparator which determines the instant at which the derivative becomes less than a predetermined threshold value.
  • said means for determining the special point of the derivative is constituted by a second differentiator and a comparator which determines the instant at which the derivative of the derivative is zero.
  • the apparatus of the invention includes a comparison signal generator which sets the value of said comparison signal:
  • the signal used for comparison purposes returns to its high value, thereby avoiding any new and untimely detection within the same temperature cycle.
  • the present invention also provides apparatus for determining the quantity of condensable substances present in a volume of gas, characterized by the fact that it comprises both apparatus as described above in which the sensitive element of the Peltier effect module is brought to the temperature of the volume of gas, and means for consulting a previously-established chart representing the relationship that exists between the quantity of condensable substances in the volume of gas and said characteristic value.
  • the present invention also provides apparatus for determining a risk of condensation on a surface in contact with a volume of gas containing condensable substances, characterized by the fact that it comprises apparatus as described above in which the sensitive surface of the Peltier effect module is brought to the temperature of the surface in contact with the volume of gas.
  • the Figure 1 apparatus comprises a first Peltier effect module 1 for measurement purposes having a sensitive element that is exposed to the air whose relative humidity is to be evaluated, and a second Peltier effect module 2 for reference purposes whose sensitive element is enclosed in an enclosure 3 which is filled with dry air.
  • the two Peltier effect modules are selected so that in the absence of water, the Seebeck component of the reference module 2 varies slightly faster than that of the measurement module 1.
  • a resistor 7 is added in series with the measurement module so that the voltage of the reference module is greater than the voltage of the measurement module.
  • the two Peltier effect modules are connected in parallel on a current source 5 which generates constant heating current and constant cooling current, during constant heating and cooling durations.
  • the operation of the current generator 5 is not under the control of external means, but takes place in regular and identical manner for both Peltier effect modules.
  • each Peltier effect module is picked up and applied to a differential amplifier 6 of high gain (about 1000), thereby determining an amplified version of the difference between the two voltages.
  • this amplified difference is referred to as the "difference".
  • the difference output by the amplifier 6 is applied to a differentiator circuit 8 constituted by a capacitor 9 and a resistor 10.
  • the output signal from the differentiator i.e. the derivative of the difference
  • a comparator 11 which compares said derivative with a threshold voltage V to generate a pulse width modulated (PWM) signal.
  • PWM pulse width modulated
  • the apparatus also includes a converter 12 for converting the PWM signal into an output voltage Vout of amplitude proportional to the duty ratio of the PWM signal.
  • This converter stage enables the apparatus described herein to control a conventional cabin regulator system which responds to different voltage values.
  • the conversion stage 12 can be omitted.
  • Figure 2 shows how the voltage across the terminals of each of the two Peltier effect modules varies over time, with the upper curve corresponding to the reference module 2 and the lower curve corresponding to the measurement module 1.
  • the measurement module 1 is subjected to a change in its voltage during the heating stages of the second and third cycles due to evaporation of the water that condensed during the cooling, while the reference Peltier effect module 2 is not subjected to any disturbance.
  • the voltage differences 13 are represented by dashed lines, the derivatives 14 by continuous lines, and the comparison signals 15 by dot-dashed lines.
  • the period of a temperature cycle is 2.8 seconds (s), and the cooling and heating cycles of each lasts for 1.4 s.
  • the first Peltier effect module and the second Peltier effect module are exposed to a volume of air, the humidity of which is so low that the air is considered as being dry.
  • the voltage difference 13 given on the right-hand scale graduated from -0.5 V to 3 V, is initially at about 2 V to 2.2 V, which corresponds to the resistive voltage due to the resistor 7.
  • the difference drops slightly, after which it returns to its initial value, in a substantially linear manner, having a slope of 0.05 V/s, as shown by its derivative, whose signal 14, plotted relative to the left-hand scale, ends up by stabilizing at a constant value of about 0.05 V.
  • the derivative signal 14 which is obtained by analog means has a time offset of about 0.15 s relative to the difference signal 13. As a result, the small drop in difference which occurs during the first tenths of a second is masked in the derivative signal 14.
  • the value of the threshold to be compared with the derivative in dry air is set to 0.05 V.
  • the comparison signal for determining the moment at which the derivative becomes less than 0.05 volts is shown in dot-dashed lines 15 using the left-hand scale graduated from -0.05 V to 0.4 V. It can be seen that throughout the cooling stage, the comparison signal is equal to the high voltage 0.21 V.
  • the comparison signal takes up its threshold value of 0.05 V.
  • the voltage of the comparison signal is returned to its high value of 0.21 V, thereby avoiding any subsequent false detection in the event of the derivative exceeding the threshold value of 0.05 V because of noise in the derivative signal.
  • a PWM signal is generated of the type shown in the top graph of Figure 9, which represents a risk of condensation that is zero or very low.
  • Figures 7 and 8 also correspond to measurements performed in dry air, i.e. with relative humidity of less than 30%, at temperatures respectively of +5 C and -5 C. These figures should be read in the same manner as that explained for Figure 6, with the exception that the mean amplitude of the difference signal 13 has a different value.
  • the derivative of the difference represented by a continuous line 14, is offset by about 0.15 s relative to the difference, as already explained.
  • This point is selected as the point characteristic of the relative humidity of the volume of air.
  • the PWM signal can be used directly to control a regulator system, or it can be converted into an output voltage Vout.
  • Figures 4 and 5 also correspond to measurements performed in a humid atmosphere, at temperatures respectively of +5 C and -5 C. These figures are to be read in the same manner as that explained for Figure 3, with the exception that the mean amplitude of the difference signal 13 takes on a different value.
  • the above-described apparatus is particularly advantageous because there is no need to provide temperature compensation for the drift of the measurement Peltier effect module since the reference Peltier effect module is subject to the same temperature drift and only the difference between the voltages across the terminals of these two modules is taken into account.
  • both Peltier effect modules can have a rest period so as to enable them to return to ambient temperature.
  • This circuit 16 comprises an RC first portion 17 generating the equivalent of the Seebeck component of the reference signal, and a second portion 18 constituted by an operational amplifier together with resistors, and suitable for generating the equivalent of the resistive component of the reference signal.
  • a stable reference signal is obtained, i.e. a signal that does not change its parameters in the event of the thermal masses 4 changing temperature, and having an amplitude of the order of 5 V.
  • the Figure 11 circuit 16 is installed as a replacement for the reference Peltier effect module.
  • a second circuit 20 constituted by an operational amplifier and resistors, including a thermistor integrated in the thermal masses 4, is connected in series with the circuit 16 to cause the signal delivered by the terminal 19 to vary as a function of temperature changes in the thermal masses 4 so that the reference signal simulated at the output 21 of the second circuit 20 varies in the same manner as the signal delivered by the measurement module 1 in the event of said module drifting in temperature.
  • the circuit 20 is a variable gain amplifier circuit whose gain increases with increasing temperature of the thermal masses 4.
  • the measurement signal from the Peltier element 1 is amplified by an amplifier circuit 22 whose sole function is to bring the amplitude of the measurement signal to a value that is comparable with that of the simulated reference signal.
  • the amplified measurement signal and the simulated reference signal are then applied to the differential amplifier 6 as described above.
  • the Figure 11 circuit 16 delivers a stable reference signal while a second circuit 23, constituted by an operational amplifier and resistors, including a thermistor integrated in the thermal masses 4, is connected in series with the measurement Peltier effect module and its amplifier circuit 22 in order to compensate for the effects of changes in the temperature of the thermal masses on the measurement signal.
  • a second circuit 23 constituted by an operational amplifier and resistors, including a thermistor integrated in the thermal masses 4, is connected in series with the measurement Peltier effect module and its amplifier circuit 22 in order to compensate for the effects of changes in the temperature of the thermal masses on the measurement signal.
  • the circuit is a variable gain amplifier circuit whose gain decreases with increasing temperature of the thermal masses.
  • the differential amplifier 6 compares two signals that are stable in the sense that these signals are not subjected to the temperature changes of the thermal masses.
  • the apparatus of the invention presents numerous advantages, including the following which are mentioned specially:

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EP98400831A 1998-04-07 1998-04-07 Méthodes pour déterminer des matières condensables dans un volume de gaz et appareils à cet effet Withdrawn EP0949504A1 (fr)

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EP98400831A EP0949504A1 (fr) 1998-04-07 1998-04-07 Méthodes pour déterminer des matières condensables dans un volume de gaz et appareils à cet effet

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EP98400831A EP0949504A1 (fr) 1998-04-07 1998-04-07 Méthodes pour déterminer des matières condensables dans un volume de gaz et appareils à cet effet

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005100964A1 (fr) * 2004-04-19 2005-10-27 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Dispositif detecteur et procede de mesure du point de rosee, sur la base d'elements peltier miniaturises
US20120250723A1 (en) * 2009-11-20 2012-10-04 Juergen Blumm System And Method For Thermal Analysis
WO2021162644A1 (fr) 2020-02-12 2021-08-19 Gorenje,D.O.O. Système de régulation environnementale permettant un fonctionnement à des températures élevées de conditions transitoires à effet de condensation réglable

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2904995A (en) * 1953-12-10 1959-09-22 Illinois Testing Laboratories Dew-point detecting device
US4579462A (en) * 1985-05-20 1986-04-01 Trans-Met Engineering, Inc. Dew point measuring apparatus
FR2702049A1 (fr) * 1993-02-24 1994-09-02 Imra Europe Sa Procédé et dispositif pour déterminer un risque de condensation d'eau sur une surface se trouvant au contact d'un volume d'air humide.

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2904995A (en) * 1953-12-10 1959-09-22 Illinois Testing Laboratories Dew-point detecting device
US4579462A (en) * 1985-05-20 1986-04-01 Trans-Met Engineering, Inc. Dew point measuring apparatus
FR2702049A1 (fr) * 1993-02-24 1994-09-02 Imra Europe Sa Procédé et dispositif pour déterminer un risque de condensation d'eau sur une surface se trouvant au contact d'un volume d'air humide.

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
VANCAUWENBERGHE O ET AL: "MICROSENSOR FOR THE PREVENTIE DETECTION OF WATER CONDENSATION: OPERATING PRINCIPLE AND INTERFACE ELECTRONICS", SENSORS AND ACTUATORS A, vol. A53, no. 1/03, May 1996 (1996-05-01), pages 304 - 308, XP000620313 *

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005100964A1 (fr) * 2004-04-19 2005-10-27 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Dispositif detecteur et procede de mesure du point de rosee, sur la base d'elements peltier miniaturises
US20120250723A1 (en) * 2009-11-20 2012-10-04 Juergen Blumm System And Method For Thermal Analysis
WO2021162644A1 (fr) 2020-02-12 2021-08-19 Gorenje,D.O.O. Système de régulation environnementale permettant un fonctionnement à des températures élevées de conditions transitoires à effet de condensation réglable

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